There has been known an approach in which, by using a polymeric carrier that forms a micelle, a medicine, genes and the like are transported to a target place in a living organism; however, with respect to the block copolymer used for this purpose, impurities have not been sufficiently removed therefrom.
Conventionally, refining processes of the synthetic high molecular compound such as a block copolymer have been carried out by using a method such as a dialysis operation, an ultrafiltration operation and a precipitating operation.
In the refining methods of the dialysis operation and ultrafiltration operation, separating and refining processes are carried out based upon a difference in molecular weights. In general, dialysis membranes and ultrafiltration films are classified into groups depending on the maximum molecular weight that is allowed to permeate; however, there are great variations in precision of molecular weights of fraction. Consequently, in the methods for refining the synthetic high molecular compound such as a block copolymer through the dialysis operation and the ultrafiltration operation, it is not possible to carry out sufficient refining processes in the case when there is not a great difference between the molecular weight of a target synthetic high molecular compound and the molecular weight of impurities. Moreover, these methods are not suitable for industrial use, and are used as refining methods in laboratories in most cases.
In contrast, the refining method using a precipitating process has been widely used as a method that is also applicable to industrial use. In this method, by using a difference in solubility to a solvent, impurities are removed so as to carry out refining processes, and this method is superior in removing low-molecular-weight components from a synthetic high molecular compound such as a block copolymer. However, in the case of impurities having greater molecular weights such as polyethylene glycols and poly(acidic amino acids), there is only a small difference in solubility to a solvent between the synthetic high molecular compound such as a block copolymer and the impurities, with the result that the high molecular compound such as a block copolymer is not sufficiently refined through the precipitating process.
As described above, impurities having great molecular weights, contained in a block copolymer, have not been sufficiently removed, and a refining method, which is suitably used for obtaining a block copolymer that is also applicable to pharmaceutical preparations and the like, has not been known.
Moreover, with respect to a micelle-forming block copolymer having amphipathic property, the conventional method for quantitatively determining impurities in the block copolymer has failed to provide sufficient analysis results.
In the conventional method, the synthetic high molecular compound such as a block copolymer is dissolved in a solvent, and analyzed by using a high speed liquid chromatography to which a gel permeation column is connected (gel permeation chromatography: GPC).
However, in the case when there is only a small difference in molecular weights among the block copolymer and impurities contained therein, it is difficult to separate them with clear peaks, failing to provide sufficient performance as quantitative determination method for impurities.
Moreover, even in the case when there is a sufficient difference in molecular weights among them, if the quantity of impurities is small, it is not possible to obtain clear peaks. This is because since the gel permeation separation mechanism utilizes molecular diffusion, a peak tends to spread on the chromatogram to cause insufficient peak heights with respect to a component that is small in quantity. Consequently, the conventional method has failed to provide a quantitative determination method with sufficient performance.
Furthermore, since the conventional method separates and quantitatively determines a main component and impurities depending upon only the difference in molecular weights, no qualitative information, such as structures and provenance of impurities, is obtained.